Most games build on other games' successes and many are downright clones. Where is the limit of imitation before legal issues come into play? Is it down to literary or graphic work like characters and storyline that cause legal problems, or can someone actually claim to own gameplay mechanics?

There are so many similar clone games out there that the rules are probably very slack or nonexistent, but I'd like to hear the views of more experienced developers / designers.

\$\begingroup\$Bear in mind that you can have legal issues whether or not you've actually done anything illegal. That is, anyone can sue you for copyright infringement at any time, and then force you to spend money defending yourself. So the legal limits aren't the only thing to worry about; be cautious of getting close (whether or not you cross the legal line) to any game from a known litigious company.\$\endgroup\$
– jhockingOct 13 '16 at 21:32

11 Answers
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I am not a lawyer and this is not legal advice. These are things I've heard many times over and have no reason to doubt.

Game mechanics cannot be copyrighted or protected in any fashion.

I could make a game called "Crystallized" that was Bejeweled, in every imaginable way, and as long as I didn't copy the art from Bejeweled (either directly, or by drawing new art that just happens to be nigh-identical) I'd be totally fine.

Game mechanics have been copied often enough that, if this weren't the case, I have no doubt we'd have heard about it by now. Game design is pretty much one giant incestuous ball of borrowing, and, honestly, is better for it.

Keep in mind that you can be sued for anything, even if you're not breaking any contracts or laws, and they might win. But I've never heard of that happening with regards to game design.

\$\begingroup\$Good answer, but: If the art is too similiar, it's illegal. The balancing is part of the art! And: Different countries have different rules!\$\endgroup\$
– AndreasJul 27 '10 at 15:03

6

\$\begingroup\$Game mechanics cannot be copyrighted but they can be patented, the Monopoly board game being one of the canonical examples. It is rare for games, especially video games, to have patented mechanics though.\$\endgroup\$
– user744Jul 28 '10 at 17:43

Other answers have covered trademarks and copyright pretty well, but do not forget patents. Many game mechanics developed in the early days of gaming are patented. The 2 that I know of are minigames while the main game loads (Ridge Racer), and jump-in multiplayer (Gauntlet). That is why you almost never see these features in any games, even though they are both great ideas. In theory if you want to use these mechanics then you have to pay a royalty to the patent holder, which could be expensive. In practice however, it is very unlikely to be enforced unless you are making a million-dollar type game.

\$\begingroup\$Do you have a source for this? I've seen a few "jump-in multiplayer" games, and the "minigames while the main game loads" is certainly not unheard of, either.\$\endgroup\$
– GnemlockAug 15 '16 at 1:43

\$\begingroup\$@Timelord64 Of course it's not unheard of. The company that held the patent, Namco, released a number of popular game franchises. The patent ran out last year, by the way. There was a significant number of articles in gaming press about it. For a source, you cou could either google "namco ridge racer galaga patent" or take a look at the patent directly...\$\endgroup\$
– EstharonAug 22 '16 at 22:21

\$\begingroup\$As I understand it lots of the patents couldn't be defended and are only there to inflate a companies patent library to make it seem like it is worth more than it is, gamesradar.com/12-unbelievable-video-game-patents here you have crazy things like a direction arrow and a glorified health bar.\$\endgroup\$
– PStagOct 8 '17 at 14:25

Game mechanics are not subject to intellectual property controls. Names can be trademarked and any game code or assets are subject to copyright protection. There is some legal precedent for going after games that are "close" (http://en.wikipedia.org/wiki/Lexulous) but that was in an Indian court so I know much less about their IP laws (see also: the various FOSS StarCraft clone projects, most threatened with suits because they had "craft" in the name).

Trademark law generally draws a distinction based on if an "average consumer" could be mislead into thinking you were related to the other property. Copyright is much simpler since it only covers concrete works. If you redrew every sprite from your favorite game they would not be violating any copyrights (but might be violating a trademark if it is something high profile).

Recently some companies have tried to bring patent suits against some big-name game companies, claiming things as outlandish as they have a patent for the concept of text chat. Time will tell as to if these are a real threat, but until your revenue is in the millions I wouldn't worry about it.

Foreword: Anything related to laws will always be in a gray area, because the case outcome ultimately comes from a handful of people.

Others have accurately pointed out that game code and assets fall under copyright law and that product, company, etc. names fall under trademark law.
However, although others have pointed out that you cannot copyright game mechanics, this isn't 100% true.

Let's look at the legal history of Tetris, a game often cloned by new game developers.

In mid-2006, and in late 1997, TTC's legal counsel sent cease and desist letters to Web sites on the basis of Tetris-type games infringing the "Tetris" trademark, trade dress, and/or "look and feel" copyright. Around 2009, TTC and Tetris Holding LLC brought legal action against BioSocia, Inc., on the grounds that BioSocia's "Blockles" game infringed on proprietary rights that were held by TTC and Tetris Holding LLC. On September 10, 2009, the legal case against BioSocia was resolved, with BioSocia agreeing to discontinue making the "Blockles" game available to the public. In May 2010, TTC's legal counsel sent cease and desist letters to Google insisting that 35 Tetris clones be removed from the Android Market. A US District Court judge ruled in June 2012 that the Tetris clone "Mino" from Xio Interactive infringed on the Tetris Company's copyrights by replicating such elements as the playfield dimensions and the shapes of the blocks.

\$\begingroup\$There are still many tetris clones on the app store. Some giving there own little twist but some are exactly the same with personalized art. So what about those, shouldn't google remove these? Or did something change in the meantime? play.google.com/store/…\$\endgroup\$
– MadmenyoJul 30 '15 at 9:11

\$\begingroup\$The source quoted by this answer seems somewhat misleading. BioSocia agreed to withdraw their game, not that it was in fact a infringement of copyright. Google withdraw the clones due to trade dress, where it was argued that because the games looked so much like Tetris, players would think it was Tetris, unfairly misrepresenting The Tetris Company itself. While a judge did rule that Mino was a copy of Tetris, The company openly admitted that they had copied Tetris. Their argument was effectively "They wouldn't give us the rights, so we changed it".\$\endgroup\$
– GnemlockAug 15 '16 at 1:54

\$\begingroup\$I have been told that a leading factor in being unable to copyright game concepts is the fact that it is too difficult to proove that the game was actually copied, and that the user did not just make their own version without addressing the original, at all. This tends to go out the window when the second developer directly admits to copying the first developer.\$\endgroup\$
– GnemlockAug 15 '16 at 1:56

Great question, what better way to ask about copyright than through games, which encompass all forms of media and IP.

First off, be aware that an idea cannot be patented.Second be aware that the copyright depends on the national law you are recommended to adhering as a natural citizen. There are for instance some difference in interpretation of Fair Use in the US vs the EU.

Fair use is the most significant limitation on the copyright holder's
exclusive rights (United States Copyright Office, 2010, para. 1)

Several basic types of IP are legally valid: copyrights, trademarks,
trade secrets, and patents. The differences depend on how the idea is
expressed. Producers should be familiar with the differences between
these, especially independent producers working with a publisher. If
the publisher is interested in your game and is ready to sign a deal,
they will most likely demand that the copyright in the game be
conveyed to them so they can create derivative products and re-
produce the product free and clear.

In conclusion, if you're doing a total and complete rip off, you're in trouble these days, but you weren't 10 years ago.

In addition there are patents. Patents for concepts in games don't apply in many countries, but due to the way these courts work, if you do business in the respective country you're in trouble. https://www.google.ch/search?q=car+racing+game+patents It's likely that you could challenge and void many of these patents in court if you have half a million to spare, per patent - or you could just pay the patent holder a fraction of that and be fine.

Finally, there are trademarks. Universal did sue Nintendo because it's apparently easy to confuse Donkey Kong and King Kong. While Universal did lose badly, Nintendo first had to be willing to enter an expensive legal battle. If you don't have the funds, you can't defend against these kinds of legal attacks.

There is some fuzziness when it comes to the law concerning things like spell names. At that point, it really comes down to how closely tied the name is to the franchise. If the brand that is being pulled from has explicit claim upon a name like that, it would likely be under trademark rather than copyright so that is what you'd want to look for.

There is this great site that I found that has an entire article on legal issues for game developers with the different types of IP explained in detail.

Hopefully that helps with the more detailed parts of avoiding IP claims.

The answers above are all pretty much spot on, unless you're copying something closely, you should be okay.

But, and this is a big but, just because you are doing everything right, it doesn't mean you won't get C&D'd, or be sued. Unfortunately, a lot of business and individuals use the legal system as a bludgeon against competitors and will often issue cease and desist orders to try and get a competing product taken down, or head straight to a lawsuit.

Much of this behaviour depends on the cost of a lawsuit and the willingness of the competitor to spend the money and fight. Not many are. Even big companies often settle when faced with a bogus patent or IP lawsuit because it's easier and less costly.

So, the short answer is that you should be okay most of the time, but you can't be guaranteed not to be the target of a frivolous lawsuit.

\$\begingroup\$I suppose the crux is that if you genuinely copy something, you are opening yourself up to trouble. If you are inspired by something, the line becomes fuzzy somewhat...\$\endgroup\$
– Ḟḹáḿíṅḡ ⱫỏḿƀíéJun 29 '15 at 15:09

\$\begingroup\$-1 1) this does not answer the question and 2) it's not the rules that are slack, is the resources of company that would need to sue al the others that are thin. If company X made a successful game, unless they're big companies like Disney, Nintendo, EA, it could cost them a lot to shut down all the clones.\$\endgroup\$
– Alexandre Vaillancourt♦Jan 4 '16 at 14:42

I have seen Modern Combat 5 use the "sapper" soldier class. It is almost identical to the "engineer" soldier class of Team Fortress 2. They are similar, as both can deploy turrets that can shoot automatically at any nearby enemy players. Both do the exact same thing, and even somewhat look alike, if that be considered copyright infringement. Team Fortress 2 had the engineer long before Modern Combat 5 had the sapper.

\$\begingroup\$This answer is not really helpful. First, this example of taking an idea from a different game is far from egregious. Second, just because one studio does it doesn't mean what they did is legal.\$\endgroup\$
– PhilippOct 13 '16 at 22:14

My personal belief is that if you have to ask the question, then you probably know in your heart that what you are doing is borderline wrong. It may or may not be legal, but to me its besides the point. If you cant be true to an art that you created then why bother.

Of course if you just want to knock down clones of popular games to make a quick buck, I doubt that anyone would bother with the hassle of legal action against you, since more often then not, if you just copied something and don't put your own spin on the issue, then it probably wont sell well enough to matter to the original.

\$\begingroup\$Although he is probably asking this in order to shape his own plans, he didn't ask about his own game, he asked about the existing games that copy each other (which is the vast majority of games.)\$\endgroup\$
– jhockingApr 23 '11 at 15:18

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\$\begingroup\$Your personal belief has little to no legal precedent. When applied to this question it is also poor advice as all art and science works by building off existing work. Example: All parody. Concrete examples: Linux OS, and the game "Braid". Writing exact (mechanical) game clones is also extremely useful for teaching how to do game programming, and is a common set of assignments. If you put a project on the market as part of your learning, then you've learned even more. Stealing copyrighted art and sound and trademarks is against the law tho.\$\endgroup\$
– Merlyn Morgan-GrahamApr 24 '12 at 17:26

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